1. Field of Endeavor
The present disclosure relates to an apparatus for controlling interior permanent magnet synchronous motor.
2. Discussion of the Related Art
This section provides background information related to the present disclosure which is not necessarily prior art.
An IPMSM (Interior Permanent Magnet Synchronous Motor), being of higher efficiency than that of an induction motor, has come to have a great limelight in terms of energy saving. However, the IPMSM is disadvantageous due to being complicated in control over the induction motor.
The IPMSM is generally controlled based on a vector control (field-oriented control). Generally, the vector control method for calculating an accurate rotation velocity of a motor is broadly used in industrial fields requiring high performance of the motor.
The vector control is classified into two methods, based on presence or absence of a position sensor, that is, a sensored vector control and a sensorless vector control.
In order to obtain a good performance of an IPMSM during vector control, motor constants (stator resistance, d-axis inductance, q-axis inductance and magnetic flux of a permanent magnet) must be essentially learned, and in order to perform a smooth start, there is a need to learn a position of a magnetic pole in a permanent magnet. Because of these requirements, the control of an IPMSM suffers from decreased versatility or generality.
FIG. 1 is a block diagram illustrating a configuration of a PWM (Pulse Width Modulation) inverter system according to prior art.
Referring to FIG. 1, the inverter system according to prior art includes a 3-phase power source unit (100) for supplying a power source to a PWM inverter (200), a PWM inverter unit (200) for converting the power source received from the 3-phase power source unit (100), and an IPMSM (300) for being operated by a voltage generated by the PWM inverter unit (200).
The PWM inverter unit (200) in turn includes a power source converting unit (210) supplying a voltage to the IPMSM (300), a current detection unit (220) detecting a current flowing in the IPMSM (300), and a controller (230) controlling a voltage and a frequency supplied to the IPMSM (300).
FIG. 2 is a conceptual block diagram illustrating a detailed configuration of a controller in FIG. 1. The controller includes a V/F pattern unit (231) generating a reference voltage (Vref) from a reference frequency (fref), and a 3-phase reference voltage conversion unit (231) generating 3-phase reference voltages (Vasref, Vbsref, Vcsref) from the reference voltage (Vref) generated by the V/F pattern unit (231).
FIG. 3 is a current waveform of an IPMSM (300) during voltage/frequency constant control by the controller of FIG. 1.
Generally, an IPMSM is conventionally controlled by a vector control method. However, in order to implement the conventional vector control method, motor constants must be basically learned and complicated equations are required.
Per contra, in a case a voltage/frequency constant control method is applied to an induction motor as illustrated in FIG. 2, an operation can be simply implemented using a simple equation even if motor constants are not known.
In a case a voltage/frequency constant control method generally applied to an induction motor is applied to an IPMSM, start of the IPMSM under no-load state is enabled by saliency of the IPMSM (A section of FIG. 3).
However, in a case a load increases under a constant state of motor velocity (output frequency), magnitude of voltage, a power semiconductor device used for PWM inverter and a current stress of the IPMSM increase due to fixation of magnitude of voltage and a current of the IPMSM being greatly shaken to increase the magnitude as in B section of FIG. 3.
As a result, operation of IPMSM suffers from a disadvantage under the simple voltage/frequency constant control method.